$($Please give me the clearly explained answer$)$ Figure $2.$ Fe$-$Ni phase diagram. Figure $2$ shows the binary Fe$-$Ni phase diagram.

a$)$ Which phases are in equilibrium and what are the amounts and compositions of these phases when T $=200$C and xFe $=0\mathrm{.}09?$

b$)$ Describe the changes in phase equilibria from $1000$C down to $200$C when the nominal composition of the Fe$-$Ni alloy is $($i$)$ xNi $=0\mathrm{.}49($ii$)$ xNi $=0\mathrm{.}10.$